by Richard Cincotta and Robert Engelman

About the authors: Richard Cincotta is an ecologist and researcher for Population Action International (PAI), a Washington, D.C.–based organization that advocates policies to slow human population growth. Robert Engelman directs the Population and Environment Program at PAI.

The world’s biological wealth is dwindling. Earth—the only location in the universe that we know supports life—is being transformed into a world that is genetically poorer. The loss is irretrievable, and its roots lie in the spectacular success of a single species: us, Homo sapiens. The disappearance of species, proceeding thousands of times faster today than in the pre-human past, is still accelerating and is likely to advance even more rapidly in the 21st century. No one can...